Magnetic tape device and head tracking servo method

ABSTRACT

The magnetic tape device includes a magnetic tape and a TMR head (servo head), in which the magnetic tape includes a non-magnetic support, and a magnetic layer including ferromagnetic powder and a binding agent on the non-magnetic support, the ferromagnetic powder is ferromagnetic hexagonal ferrite powder, an intensity ratio of a peak intensity Int(110) of a diffraction peak of a (110) plane with respect to a peak intensity Int(114) of a diffraction peak of a (114) plane of a hexagonal ferrite crystal structure obtained by an X-ray diffraction analysis of the magnetic layer by using an In-Plane method is 0.5 to 4.0, and a vertical direction squareness ratio of the magnetic tape is 0.65 to 1.00.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C 119 to Japanese PatentApplication No. 2017-065694 filed on Mar. 29, 2017. The aboveapplication is hereby expressly incorporated by reference, in itsentirety, into the present application.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a magnetic tape device and a headtracking servo method.

2. Description of the Related Art

Magnetic recording is used as a method of recording information on arecording medium. In the magnetic recording, information is recorded ona magnetic recording medium as a magnetized pattern. Informationrecorded on a magnetic recording medium is reproduced by reading amagnetic signal obtained from the magnetized pattern by a magnetic head.As a magnetic head used for such reproducing, various magnetic headshave been proposed (for example, see JP2004-185676A).

SUMMARY OF THE INVENTION

An increase in recording capacity (high capacity) of a magneticrecording medium is required in accordance with a great increase ininformation content in recent years. As means for realizing highcapacity, a technology of increasing a recording density of a magneticrecording medium is used. However, as the recording density increases, amagnetic signal (specifically, a leakage magnetic field) obtained from amagnetic layer tends to become weak. Accordingly, it is desired that ahigh-sensitivity magnetic head capable of reading a weak signal withexcellent sensitivity is used as a reproducing head. Regarding thesensitivity of the magnetic head, it is said that a magnetoresistive(MR) head using a magnetoresistance effect as an operating principle hasexcellent sensitivity, compared to an inductive head used in the relatedart.

As the MR head, an anisotropic magnetoresistive (AMR) head and a giantmagnetoresistive (GMR) head are known as disclosed in a paragraph 0003of JP2004-185676A. The GMR head is an MR head having excellentsensitivity than that of the AMR head. In addition, a tunnelmagnetoresistive (TMR) head disclosed in a paragraph 0004 and the likeof JP2004-185676A is an MR head having a high possibility of realizinghigher sensitivity.

Meanwhile, a recording and reproducing system of the magnetic recordingis broadly divided into a levitation type and a sliding type. A magneticrecording medium in which information is recorded by the magneticrecording is broadly divided into a magnetic disk and a magnetic tape.Hereinafter, a drive including a magnetic disk as a magnetic recordingmedium is referred to as a “magnetic disk device” and a drive includinga magnetic tape as a magnetic recording medium is referred to as a“magnetic tape device”.

The magnetic disk device is generally called a hard disk drive (HDD) anda levitation type recording and reproducing system is used. In themagnetic disk device, a shape of a surface of a magnetic head sliderfacing a magnetic disk and a head suspension assembly that supports themagnetic head slider are designed so that a predetermined intervalbetween a magnetic disk and a magnetic head can be maintained with airflow at the time of rotation of the magnetic disk. In such a magneticdisk device, information is recorded and reproduced in a state where themagnetic disk and the magnetic head do not come into contact with eachother. The recording and reproducing system described above is thelevitation type. On the other hand, a sliding type recording andreproducing system is used in the magnetic tape device. In the magnetictape device, a surface of a magnetic layer of a magnetic tape and amagnetic head come into contact with each other and slide on each other,at the time of the recording and reproducing information.

JP2004-185676A proposes usage of the TMR head as a reproducing head forreproducing information in the magnetic disk device. On the other hand,the usage of the TMR head as a reproducing head in the magnetic tapedevice is currently still in a stage where the future usage thereof isexpected, and the usage thereof is not yet practically realized.

However, in the magnetic tape, information is normally recorded on adata band of the magnetic tape. Accordingly, data tracks are formed inthe data band. As means for realizing high capacity of the magnetictape, a technology of disposing the larger amount of data tracks in awidth direction of the magnetic tape by narrowing the width of the datatrack to increase recording density is used. However, in a case wherethe width of the data track is narrowed and the recording and/orreproduction of information is performed by transporting the magnetictape in the magnetic tape device, it is difficult that a magnetic headproperly follows the data tracks in accordance with the position changeof the magnetic tape, and errors may easily occur at the time ofrecording and/or reproduction. Thus, as means for preventing occurrenceof such errors, a method of forming a servo pattern in the magneticlayer and performing head tracking servo has been recently proposed andpractically used. In a magnetic servo type head tracking servo amonghead tracking servos, a servo pattern is formed in a magnetic layer of amagnetic tape, and this servo pattern is read by a servo head to performhead tracking servo. The head tracking servo is to control a position ofa magnetic head in the magnetic tape device. The head tracking servo ismore specifically performed as follows.

First, a servo head reads a servo pattern to be formed in a magneticlayer (that is, reproduces a servo signal). A position of a magnetichead in a magnetic tape device is controlled in accordance with a valueobtained by reading the servo pattern. Accordingly, in a case oftransporting the magnetic tape in the magnetic tape device for recordingand/or reproducing information, it is possible to increase an accuracyof the magnetic head following the data track, even in a case where theposition of the magnetic tape is changed. For example, even in a casewhere the position of the magnetic tape is changed in the widthdirection with respect to the magnetic head, in a case of recordingand/or reproducing information by transporting the magnetic tape in themagnetic tape device, it is possible to control the position of themagnetic head of the magnetic tape in the width direction in themagnetic tape device, by performing the head tracking servo. By doingso, it is possible to properly record information in the magnetic tapeand/or properly reproduce information recorded on the magnetic tape inthe magnetic tape device.

The servo pattern is formed by magnetizing a specific position of themagnetic layer. A plurality of regions including a servo pattern(referred to as “servo bands”) are generally present in the magnetictape capable of performing the head tracking servo along a longitudinaldirection. A region interposed between two servo bands is referred to asa data band. The recording of information is performed on the data bandand a plurality of data tracks are formed in each data band along thelongitudinal direction. In order to realize high capacity of themagnetic tape, it is preferable that the larger number of the data bandswhich are regions where information is recorded are present in themagnetic layer. As means for that, a technology of increasing apercentage of the data bands occupying the magnetic layer by narrowingthe width of the servo band which is not a region in which informationis recorded is considered. Since a read track width of the servo patternbecomes narrow, in a case where the width of the servo band becomesnarrow, reading accuracy of the servo pattern tends to decrease. As aresult, a Signal-to-Noise-Ratio (SNR) at the time of reading a servopattern tends to decrease. In regards to this point, the inventors haveconsidered that, it is desired to use a magnetic head having highsensitivity as the servo head, in order to increase an SNR at the timeof reading a servo pattern. As a magnetic head for this, the inventorsfocused on a TMR head which has been proposed to be used as areproducing head in the magnetic disk device in JP2004-185676A. Asdescribed above, the usage of the TMR head in the magnetic tape deviceis still in a stage where the future use thereof as a reproducing headfor reproducing information is expected, and the usage of the TMR headas the servo head has not even proposed yet. With respect to this, theinventors have thought that, it is possible to deal with realization ofhigher sensitivity of the future magnetic tape, by using the TMR head asthe servo head in the magnetic tape device which performs the headtracking servo. In addition, the inventors have investigated regarding afurther increase in SNR in a case of reading a servo pattern by usingthe TMR head as a servo head. This is because, it is thought that it ispossible to improve accuracy of the magnetic head following the datatrack by the head tracking servo, as the SNR at the time of reading aservo pattern increases.

An object of the invention is to provide a magnetic tape device in whicha TMR head is mounted as a servo head and a servo pattern written on amagnetic tape can be read at a high SNR.

According to one aspect of the invention, there is provided a magnetictape device comprising: a magnetic tape; and a servo head, in which theservo head is a magnetic head (hereinafter, also referred to as a “TMRhead”) including a tunnel magnetoresistance effect type element(hereinafter, also referred to as a “TMR element”) as a servo patternreading element, the magnetic tape includes a non-magnetic support, anda magnetic layer including ferromagnetic powder and a binding agent onthe non-magnetic support, the magnetic layer includes the servo pattern,the ferromagnetic powder is ferromagnetic hexagonal ferrite powder, anintensity ratio (Int(110)/Int(114); hereinafter, also referred to as“X-ray diffraction (XRD) intensity ratio) of a peak intensity Int(110)of a diffraction peak of a (110) plane with respect to a peak intensityInt(114) of a diffraction peak of a (114) plane of a hexagonal ferritecrystal structure obtained by an X-ray diffraction analysis of themagnetic layer by using an In-Plane method is 0.5 to 4.0, and a verticaldirection squareness ratio of the magnetic tape is 0.65 to 1.00.

According to another aspect of the invention, there is provided a headtracking servo method comprising: reading a servo pattern of a magneticlayer of a magnetic tape by a servo head in a magnetic tape device, inwhich the servo head is a magnetic head including a tunnelmagnetoresistance effect type element as a servo pattern readingelement, the magnetic tape includes a non-magnetic support, and amagnetic layer including ferromagnetic powder and a binding agent on thenon-magnetic support, the magnetic layer includes the servo pattern, theferromagnetic powder is ferromagnetic hexagonal ferrite powder, anintensity ratio (Int(110)/Int(114)) of a peak intensity Int(110) of adiffraction peak of a (110) plane with respect to a peak intensityInt(114) of a diffraction peak of a (114) plane of a hexagonal ferritecrystal structure obtained by an X-ray diffraction analysis of themagnetic layer by using an In-Plane method is 0.5 to 4.0, and a verticaldirection squareness ratio of the magnetic tape is 0.65 to 1.00.

One aspect of the magnetic tape device and the head tracking servomethod is as follows.

In one aspect, the vertical direction squareness ratio is 0.65 to 0.90.

In one aspect, a center line average surface roughness Ra measuredregarding a surface of the magnetic layer (hereinafter, also referred toas a “magnetic layer surface roughness Ra”) is equal to or smaller than2.5 nm.

In one aspect, the magnetic tape includes a non-magnetic layer includingnon-magnetic powder and a binding agent between the non-magnetic supportand the magnetic layer.

According to one aspect of the invention, it is possible to read a servopattern of the magnetic layer of the magnetic tape with the TMR head ata high SNR.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of disposition of data bands and servo bands.

FIG. 2 shows a servo pattern disposition example of a linear-tape-open(LTO) Ultrium format tape.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Magnetic Tape Device

One aspect of the invention relates to a magnetic tape device including:a magnetic tape; and a servo head, in which the servo head is a magnetichead including a tunnel magnetoresistance effect type element as a servopattern reading element, the magnetic tape includes a non-magneticsupport, and a magnetic layer including ferromagnetic powder and abinding agent on the non-magnetic support, the magnetic layer includes aservo pattern, the ferromagnetic powder is ferromagnetic hexagonalferrite powder, an intensity ratio (Int(110)/Int(114)) of a peakintensity Int(110) of a diffraction peak of a (110) plane with respectto a peak intensity Int(114) of a diffraction peak of a (114) plane of ahexagonal ferrite crystal structure obtained by an X-ray diffractionanalysis of the magnetic layer by using an In-Plane method is 0.5 to4.0, and a vertical direction squareness ratio of the magnetic tape is0.65 to 1.00.

In the invention and the specification, a “surface of a magnetic layer”of a magnetic tape is identical to a surface of a magnetic recordingmedium on a magnetic layer side. In the invention and the specification,the “ferromagnetic hexagonal ferrite powder” means an aggregate of aplurality of ferromagnetic hexagonal ferrite particles. Theferromagnetic hexagonal ferrite particles are ferromagnetic particleshaving a hexagonal ferrite crystal structure. Hereinafter, particles(ferromagnetic hexagonal ferrite particles) configuring theferromagnetic hexagonal ferrite powder are also referred to as“hexagonal ferrite particles” or simply “particles”. The “aggregate” notonly includes an aspect in which particles configuring the aggregatedirectly come into contact with each other, but also includes an aspectin which a binding agent, an additive, or the like is interposed betweenthe particles. The points described above are also applied to variouspowders such as non-magnetic powder of the invention and thespecification, in the same manner.

In the invention and the specification, the description regardingdirections and angles (for example, vertical, orthogonal, parallel, andthe like) includes a range of errors allowed in the technical field ofthe invention, unless otherwise noted. For example, the range of errorsmeans a range of less than ±10° from an exact angle, and is preferablywithin ±5° and more preferably within ±3°.

The magnetic tape device includes a TMR head as a servo head. This cancontribute to improvement of the SNR at the time of reading a servopattern. In addition, the inventors have thought that the verticaldirection squareness ratio and the XRD intensity ratio set to be in theranges described above contribute to the reading of a servo patternwritten in the magnetic layer of the magnetic tape in the magnetic tapedevice by using the TMR head at a high SNR. This point will be furtherdescribed hereinafter.

The magnetic tape of the magnetic tape device includes ferromagnetichexagonal ferrite powder in the magnetic layer. The inventors havesurmised that particles affecting magnetic properties of theferromagnetic hexagonal ferrite powder (aggregate of particles)(hereinafter, also referred to as “former particles”) and particleswhich are considered not to affect or slightly affects the magneticproperties thereof (hereinafter, also referred to as “latter particles”)are included in the ferromagnetic hexagonal ferrite powder included inthe magnetic layer. It is considered that the latter particles are, forexample, fine particles generated due to partial chipping of particlesdue to a dispersion process performed at the time of preparing amagnetic layer forming composition.

The inventors have thought that, in the particles included in theferromagnetic hexagonal ferrite powder included in the magnetic layer,the former particles are particles causing the diffraction peak in theX-ray diffraction analysis using the In-Plane method, and since thelatter particles are fine, the latter particles do not or hardly affectthe diffraction peak. Accordingly, it is surmised that it is possible tocontrol a state of the particles affecting the magnetic properties ofthe ferromagnetic hexagonal ferrite powder present in the magneticlayer, based on the intensity of the diffraction peak caused by theX-ray diffraction analysis of the magnetic layer using the In-Planemethod. The inventors have thought that the XRD intensity ratio whichwill be described later specifically is an index regarding this point.

Meanwhile, the vertical direction squareness ratio is a ratio ofresidual magnetization with respect to saturated magnetization measuredin a direction vertical to the surface of the magnetic layer and thisvalue decreases, as a value of the residual magnetization decreases. Itis surmised that, since the latter particles are fine and hardly holdmagnetization, as a large amount of the latter particles is included inthe magnetic layer, the vertical direction squareness ratio tends todecrease. Accordingly, the inventors have thought that the verticaldirection squareness ratio may be an index for the amount of the latterparticles (fine particles) present in the magnetic layer. It is thoughtthat, as the amount of such fine particles present in the magnetic layerdecreases, the magnetic properties of the ferromagnetic hexagonalferrite powder are improved.

It is surmised that, in the magnetic tape included in the magnetic tapedevice, the vertical direction squareness ratio and the XRD intensityratio respectively in the ranges described above contribute to thereading of a servo pattern written in the magnetic layer of the magnetictape at a high SNR. The inventors have surmised that the reading at ahigh SNR can be realized by decreasing the amount of the latterparticles (fine particles) present in the magnetic layer and controllinga state of the former particles present in the magnetic layer.

The above description is a surmise of the inventors regarding thereading of a servo pattern written in the magnetic layer of the magnetictape at a high SNR, in the magnetic tape device.

However, the above descriptions are merely a surmise of the inventorsand the invention is not limited thereto.

Hereinafter, the magnetic tape device will be described morespecifically.

Magnetic Tape

XRD Intensity Ratio

The magnetic tape includes ferromagnetic hexagonal ferrite powder in themagnetic layer. The XRD intensity ratio is obtained by the X-raydiffraction analysis of the magnetic layer including the ferromagnetichexagonal ferrite powder by using the In-Plane method. Hereinafter, theX-ray diffraction analysis performed by using the In-Plane method isalso referred to as “In-Plane XRD”. The In-Plane XRD is performed byirradiating the surface of the magnetic layer with the X-ray by using athin film X-ray diffraction device under the following conditions. Ameasurement direction is a longitudinal direction of the magnetic tape.

Cu ray source used (output of 45 kV, 200 mA)

Scan conditions: 0.05 degree/step, 0.1 degree/min in a range of 20 to 40degrees

Optical system used: parallel optical system

Measurement method: 20× scan (X-ray incidence angle of 0.25°)

The values of the conditions are set values of the thin film X-raydiffraction device. As the thin film X-ray diffraction device, awell-known device can be used. As an example of the thin film X-raydiffraction device, Smart Lab manufactured by Rigaku Corporation. Asample to be subjected to the In-Plane XRD analysis is a tape sample cutout from the magnetic tape which is a measurement target, and the sizeand the shape thereof are not limited, as long as the diffraction peakwhich will be described later can be confirmed.

As a method of the X-ray diffraction analysis, thin film X-raydiffraction and powder X-ray diffraction are used. In the powder X-raydiffraction, the X-ray diffraction of the powder sample is measured,whereas, according to the thin film X-ray diffraction, the X-raydiffraction of a layer or the like formed on a substrate can bemeasured. The thin film X-ray diffraction is classified into theIn-Plane method and an Out-Of-Plane method. The X-ray incidence angle atthe time of the measurement is 5.00° to 90.00° in a case of theOut-Of-Plane method, and is generally 0.20° to 0.50°, in a case of theIn-Plane method. In the In-Plane XRD of the invention and thespecification, the X-ray incidence angle is 0.25° as described above. Inthe In-Plane method, the X-ray incidence angle is smaller than that inthe Out-Of-Plane method, and thus, a depth of penetration of the X-rayis shallow. Accordingly, according to the X-ray diffraction analysis byusing the In-Plane method (In-Plane XRD), it is possible to perform theX-ray diffraction analysis of a surface part of a measurement targetsample. Regarding the tape sample, according to the In-Plane XRD, it ispossible to perform the X-ray diffraction analysis of the magneticlayer. The XRD intensity ratio is an intensity ratio (Int(110)/Int(114))of a peak intensity Int(110) of a diffraction peak of a (110) plane withrespect to a peak intensity Int(114) of a diffraction peak of a (114)plane of a hexagonal ferrite crystal structure, in X-ray diffractionspectra obtained by the In-Plane XRD. The term Int is used asabbreviation of intensity. In the X-ray diffraction spectra obtained byIn-Plane XRD (vertical axis: intensity, horizontal axis: diffractionangle 20× (degree)), the diffraction peak of the (114) plane is a peakat which the 20× is detected at 33 to 36 degrees, and the diffractionpeak of the (110) plane is a peak at which the 20× is detected at 29 to32 degrees.

Among the diffraction plane, the (114) plane having a hexagonal ferritecrystal structure is positioned close to particles (hexagonal ferriteparticles) of the ferromagnetic hexagonal ferrite powder in aneasy-magnetization axial direction (c axis direction). In addition the(110) plane having a hexagonal ferrite crystal structure is positionedin a direction orthogonal to the easy-magnetization axial direction.

The inventors have surmised that, in the X-ray diffraction spectraobtained by the In-Plane XRD, as the intensity ratio (Int(110)/Int(114);XRD intensity ratio) of the peak intensity Int(110) of the diffractionpeak of a (110) plane with respect to the peak intensity Int(114) of thediffraction peak of the (114) plane of a hexagonal ferrite crystalstructure increases, a large number of the former particles present in astate where a direction orthogonal to the easy-magnetization axialdirection is closer to a parallel state with respect to the surface ofthe magnetic layer is present in the magnetic layer, and as the XRDintensity ratio decreases, a small amount of the former particlespresent in such a state is present in the magnetic layer. It is thoughtthat a state where the XRD intensity ratio is 0.5 to 4.0 means a statewhere the former particles are suitably aligned in the magnetic layer.The inventors have surmised that this contributes to an increase in SNRat the time of reading a servo pattern with the TMR head.

The XRD intensity ratio is preferably equal to or smaller than 3.5 andmore preferably equal to or smaller than 3.0, from a viewpoint offurther increasing the SNR. From the same viewpoint, the XRD intensityratio is preferably equal to or greater than 0.7 and more preferablyequal to or greater than 1.0. The XRD intensity ratio can be, forexample, controlled in accordance with process conditions of anorientation process performed in a manufacturing step of the magnetictape. As the orientation process, the homeotropic alignment process ispreferably performed. The homeotropic alignment process can bepreferably performed by applying a magnetic field vertically to thesurface of a coating layer of a magnetic layer forming composition in awet state (undried state). As the orientation conditions are reinforced,the value of the XRD intensity ratio tends to increase. As the processconditions of the orientation process, magnetic field strength of theorientation process is used. The process conditions of the orientationprocess are not particularly limited. The process conditions of theorientation process may be set so as that the XRD intensity ratio of 0.5to 4.0 can be realized. As an example, the magnetic field strength ofthe homeotropic alignment process can be 0.10 to 0.80 T or 0.10 to 0.60T. As dispersibility of the ferromagnetic hexagonal ferrite powder inthe magnetic layer forming composition increases, the value of the XRDintensity ratio tends to increase by the homeotropic alignment process.

Vertical Direction Squareness Ratio

The vertical direction squareness ratio is a squareness ratio measuredregarding a magnetic tape in a vertical direction. The “verticaldirection” described regarding the squareness ratio is a directionorthogonal to the surface of the magnetic layer. That is, regarding themagnetic tape, the vertical direction is a direction orthogonal to alongitudinal direction of the magnetic tape. The vertical directionsquareness ratio is measured by using an oscillation sample typemagnetic-flux meter. Specifically, the vertical direction squarenessratio of the invention and the specification is a value obtained bysweeping an external magnetic field in the magnetic tape at ameasurement temperature of 23° C.±1° C. in the oscillation sample typemagnetic-flux meter, under conditions of a maximum external magneticfield of 1194 kA/m (15 kOe) and a scan speed of 4.8 kA/m/sec (60Oe/sec), and is a value after diamagnetic field correction. Themeasurement value is obtained as a value obtained by subtractingmagnetization of a sample probe of the oscillation sample typemagnetic-flux meter as background noise.

The vertical direction squareness ratio of the magnetic tape is equal toor greater than 0.65. The inventors have surmised that the verticaldirection squareness ratio of the magnetic tape is an index for thepresence amount of the latter particles (fine particles) describedabove. It is thought that, in the magnetic layer in which the verticaldirection squareness ratio of the magnetic tape is equal to or greaterthan 0.65, the presence amount of such fine particles is small. Theinventors have surmised that this contributes to an increase in SNR atthe time of reading a servo pattern of the magnetic layer with the TMRhead. From a viewpoint of further increasing the SNR, the verticaldirection squareness ratio is preferably equal to or greater than 0.70,more preferably equal to or greater than 0.73, and even more preferablyequal to or greater than 0.75. In addition, in principle, a maximumvalue of the squareness ratio is 1.00. Accordingly, the verticaldirection squareness ratio of the magnetic tape is equal to or smallerthan 1.00. The vertical direction squareness ratio may be, for example,equal to or smaller than 0.95, equal to or smaller than 0.90, equal toor smaller than 0.87, or equal to or smaller than 0.85. However, it isthought that, a great value of the vertical direction squareness ratiois preferable, from a viewpoint of decreasing the amount of the latterfine particles in the magnetic layer and increasing the SNR. Therefore,the vertical direction squareness ratio may be greater than the valueexemplified above.

The inventors have considered that, in order to set the verticaldirection squareness ratio to be equal to or greater than 0.65, it ispreferable to prevent occurrence of fine particles due to partialchipping of the particles in a preparation step of the magnetic layerforming composition. A specific method for preventing the occurrence ofchipping will be described later.

Next, the magnetic layer and the like included in the magnetic tape willbe described more specifically.

Magnetic Layer

Ferromagnetic Powder

The magnetic layer of the magnetic tape includes ferromagnetic hexagonalferrite powder as ferromagnetic powder. Regarding the ferromagnetichexagonal ferrite powder, a magnetoplumbite type (also referred to as an“M type”), a W type, a Y type, and a Z type are known as the crystalstructure of the hexagonal ferrite. The ferromagnetic hexagonal ferritepowder included in the magnetic layer may have any crystal structure. Inaddition, an iron atom and a divalent metal atom are included in thecrystal structure of the hexagonal ferrite, as constituent atoms. Thedivalent metal atom is a metal atom which may become divalent cations asions, and examples thereof include a barium atom, a strontium atom, analkaline earth metal atom such as calcium atom, and a lead atom. Forexample, the hexagonal ferrite including a barium atom as the divalentmetal atom is a barium ferrite, and the hexagonal ferrite including astrontium atom is a strontium ferrite. In addition, the hexagonalferrite may be a mixed crystal of two or more hexagonal ferrites. As anexample of the mixed crystal, a mixed crystal of the barium ferrite andthe strontium ferrite can be used.

As an index for a particle size of the ferromagnetic hexagonal ferritepowder, an activation volume can be used. The “activation volume” is aunit of magnetization reversal. Regarding the activation volumedescribed in the invention and the specification, magnetic field sweeprates of a coercivity Hc measurement part at time points of 3 minutesand 30 minutes are measured by using an oscillation sample typemagnetic-flux meter in an environment of an atmosphere temperature of23° C.±1° C., and the activation volume is a value acquired from thefollowing relational expression of Hc and an activation volume V.

Hc=2Ku/Ms{1−[(kT/KuV)ln(At/0.693)]^(1/2)}

[In the expression, Ku: anisotropy constant, Ms: saturationmagnetization, k: Boltzmann's constant, T: absolute temperature, V:activation volume, A: spin precession frequency, and t: magnetic fieldreversal time]

As a method for achieving high-density recording, a method of decreasinga particle size of ferromagnetic powder included in a magnetic layer andincreasing a filling percentage of the ferromagnetic powder of themagnetic layer is used. From this viewpoint, the activation volume ofthe ferromagnetic hexagonal ferrite powder is preferably equal to orsmaller than 2,500 nm³, more preferably equal to or smaller than 2,300nm³, and even more preferably equal to or smaller than 2,000 nm³.Meanwhile, from a viewpoint of stability of magnetization, theactivation volume is, for example, preferably equal to or greater than800 nm³, more preferably equal to or greater than 1,000 nm³, and evenmore preferably equal to or greater than 1,200 nm³. An activation volumeof the ferromagnetic hexagonal ferrite powder used for preparing themagnetic layer forming composition (hereinafter, also referred to as“raw material powder”) and an activation volume of the ferromagnetichexagonal ferrite powder in the magnetic layer formed by using theprepared magnetic layer forming composition may be the same as eachother or different from each other.

The shape of the particle configuring the ferromagnetic hexagonalferrite powder is specified by imaging the ferromagnetic hexagonalferrite powder at a magnification ratio of 100,000 with a transmissionelectron microscope, and tracing an outline of a particle (primaryparticle) with a digitizer on a particle image obtained by printing theimage on printing paper so that the total magnification of 500,000. Theprimary particle is an independent particle which is not aggregated. Theimaging with a transmission electron microscope is performed by a directmethod with a transmission electron microscope at an accelerationvoltage of 300 kV. The transmission electron microscope observation andmeasurement can be, for example, performed with a transmission electronmicroscope H-9000 manufactured by Hitachi, Ltd. and image analysissoftware KS-400 manufactured by Carl Zeiss. Regarding the shape of theparticle configuring the ferromagnetic hexagonal ferrite powder, a“planar shape” is a shape having two plate surfaces facing each other.Meanwhile, among the shapes of the particles not having such a platesurface, a shape having distinguished long axis and short axis is an“elliptical shape”. The long axis is determined as an axis (linear line)having the longest length of the particle. In contrast, the short axisis determined as an axis having the longest length of the particle in alinear line orthogonal to the long axis. A shape not havingdistinguished long axis and short axis, that is, a shape in which thelength of the long axis is the same as the length of the short axis is a“spherical shape”. From the shapes, a shape in which the long axis andthe short axis are hardly specified, is called an undefined shape. Theimaging with a transmission electron microscope for specifying theshapes of the particles is performed without performing the orientationprocess with respect to the imaging target powder. The shape of the rawmaterial powder used for the preparation of the magnetic layer formingcomposition and the ferromagnetic hexagonal ferrite powder included inthe magnetic layer may be any one of the planar shape, the ellipticalshape, the spherical shape, and the undefined shape.

An average particle size of various powders disclosed in the inventionand the specification is an arithmetical mean of the values obtainedregarding arbitrarily extracted 500 particles by using the particleimage which is captured as described above. The average particle sizeshown in the examples which will be described later is a value obtainedby using transmission electron microscope H-9000 manufactured byHitachi, Ltd. as the transmission electron microscope and image analysissoftware KS-400 manufactured by Carl Zeiss as the image analysissoftware.

For details of the ferromagnetic hexagonal ferrite powder, descriptionsdisclosed in paragraphs 0134 to 0136 of JP2011-216149A can be referredto, for example.

The content (filling percentage) of the ferromagnetic hexagonal ferritepowder in the magnetic layer is preferably 50 to 90 mass % and morepreferably 60 to 90 mass %. The components other than the ferromagnetichexagonal ferrite powder of the magnetic layer are at least a bindingagent, and one or more kinds of additives may be arbitrarily included. Ahigh filling percentage of the ferromagnetic hexagonal ferrite powder inthe magnetic layer is preferable from a viewpoint of improvementrecording density.

Binding Agent

The magnetic tape is a coating type magnetic tape, and the magneticlayer includes a binding agent together with the ferromagnetic powder.As the binding agent, one or more kinds of resin is used. The resin maybe a homopolymer or a copolymer. As the binding agent, various resinsnormally used as a binding agent of the coating type magnetic recordingmedium can be used. For example, as the binding agent, a resin selectedfrom a polyurethane resin, a polyester resin, a polyamide resin, a vinylchloride resin, an acrylic resin obtained by copolymerizing styrene,acrylonitrile, or methyl methacrylate, a cellulose resin such asnitrocellulose, an epoxy resin, a phenoxy resin, and a polyvinylalkylalresin such as polyvinyl acetal or polyvinyl butyral can be used alone ora plurality of resins can be mixed with each other to be used. Amongthese, a polyurethane resin, an acrylic resin, a cellulose resin, and avinyl chloride resin are preferable. These resins can be used as thebinding agent even in the non-magnetic layer and/or a back coating layerwhich will be described later. For the binding agent described above,description disclosed in paragraphs 0028 to 0031 of JP2010-24113A can bereferred to. An average molecular weight of the resin used as thebinding agent can be, for example, 10,000 to 200,000 as a weight-averagemolecular weight. The weight-average molecular weight of the inventionand the specification is a value obtained by performing polystyreneconversion of a value measured by gel permeation chromatography (GPC).As the measurement conditions, the following conditions can be used. Theweight-average molecular weight shown in examples which will bedescribed later is a value obtained by performing polystyrene conversionof a value measured under the following measurement conditions.

GPC device: HLC-8120 (manufactured by Tosoh Corporation)

Column: TSK gel Multipore HXL-M (manufactured by Tosoh Corporation, 7.8mmID (inner diameter)×30.0 cm)

Eluent: Tetrahydrofuran (THF)

In addition, a curing agent can also be used together with the bindingagent. As the curing agent, in one aspect, a thermosetting compoundwhich is a compound in which a curing reaction (crosslinking reaction)proceeds due to heating can be used, and in another aspect, aphotocurable compound in which a curing reaction (crosslinking reaction)proceeds due to light irradiation can be used. At least a part of thecuring agent is included in the magnetic layer in a state of beingreacted (crosslinked) with other components such as the binding agent,by proceeding the curing reaction in the magnetic layer forming step.The preferred curing agent is a thermosetting compound, polyisocyanateis suitable. For details of the polyisocyanate, descriptions disclosedin paragraphs 0124 and 0125 of JP2011-216149A can be referred to, forexample. The amount of the curing agent can be, for example, 0 to 80.0parts by mass with respect to 100.0 parts by mass of the binding agentin the magnetic layer forming composition, and is preferably 50.0 to80.0 parts by mass, from a viewpoint of improvement of strength of eachlayer such as the magnetic layer.

Other Components

The magnetic layer may include one or more kinds of additives, ifnecessary, together with the various components described above. As theadditives, a commercially available product can be suitably selected andused according to the desired properties. Alternatively, a compoundsynthesized by a well-known method can be used as the additives. As theadditives, the curing agent described above is used as an example. Inaddition, examples of the additive which can be included in the magneticlayer include a non-magnetic filler, a lubricant, a dispersing agent, adispersing assistant, an antibacterial agent, an antistatic agent, anantioxidant, and carbon black. The non-magnetic filler is identical tothe non-magnetic powder. As the non-magnetic filler, a non-magneticfiller (hereinafter, referred to as a “projection formation agent”)which can function as a projection formation agent which formsprojections suitably protruded from the surface of the magnetic layer,and a non-magnetic filler (hereinafter, referred to as an “abrasive”)which can function as an abrasive can be used.

Non-Magnetic Filler

As the projection formation agent which is one aspect of thenon-magnetic filler, various non-magnetic powders normally used as aprojection formation agent can be used. These may be inorganicsubstances or organic substances. In one aspect, from a viewpoint ofhomogenization of friction properties, particle size distribution of theprojection formation agent is not polydispersion having a plurality ofpeaks in the distribution and is preferably monodisperse showing asingle peak. From a viewpoint of availability of monodisperse particles,the projection formation agent is preferably powder of inorganicsubstances (inorganic powder). Examples of the inorganic powder includepowder of inorganic oxide such as metal oxide, metal carbonate, metalsulfate, metal nitride, metal carbide, and metal sulfide, and powder ofinorganic oxide is preferable. The projection formation agent is morepreferably colloidal particles and even more preferably inorganic oxidecolloidal particles. In addition, from a viewpoint of availability ofmonodisperse particles, the inorganic oxide configuring the inorganicoxide colloidal particles are preferably silicon dioxide (silica). Theinorganic oxide colloidal particles are more preferably colloidal silica(silica colloidal particles). In the invention and the specification,the “colloidal particles” are particles which are not precipitated anddispersed to generate a colloidal dispersion, in a case where 1 g of theparticles is added to 100 mL of at least one organic solvent of at leastmethyl ethyl ketone, cyclohexanone, toluene, or ethyl acetate, or amixed solvent including two or more kinds of the solvent described aboveat an arbitrary mixing ratio. The average particle size of the colloidalparticles is a value obtained by a method disclosed in a paragraph 0015of JP2011-048878A as a measurement method of an average particlediameter. In addition, in another aspect, the projection formation agentis preferably carbon black.

An average particle size of the projection formation agent is, forexample, 30 to 300 nm and is preferably 40 to 200 nm.

The abrasive which is another aspect of the non-magnetic filler ispreferably non-magnetic powder having Mohs hardness exceeding 8 and morepreferably non-magnetic powder having Mohs hardness equal to or greaterthan 9. A maximum value of Mohs hardness is 10 of diamond. Specifically,powders of alumina (Al₂O₃), silicon carbide, boron carbide (B₄C), SiO₂,TiC, chromium oxide (Cr₂O₃), cerium oxide, zirconium oxide (ZrO₂), ironoxide, diamond, and the like can be used, and among these, aluminapowder such as α-alumina and silicon carbide powder are preferable. Inaddition, regarding the particle size of the abrasive, a specificsurface area which is an index for the particle size is, for example,equal to or greater than 14 m²/g, and is preferably 16 m²/g and morepreferably 18 m²/g. Further, the specific surface area of the abrasivecan be, for example, equal to or smaller than 40 m²/g. The specificsurface area is a value obtained by a nitrogen adsorption method (alsoreferred to as a Brunauer-Emmett-Teller (BET) 1 point method), and is avalue measured regarding primary particles. Hereinafter, the specificsurface area obtained by such a method is also referred to as a BETspecific surface area.

In addition, from a viewpoint that the projection formation agent andthe abrasive can exhibit the functions thereof in more excellent manner,the content of the projection formation agent of the magnetic layer ispreferably 1.0 to 4.0 parts by mass and more preferably 1.5 to 3.5 partsby mass with respect to 100.0 parts by mass of the ferromagnetic powder.Meanwhile, the content of the magnetic layer is preferably 1.0 to 20.0parts by mass, more preferably 3.0 to 15.0 parts by mass, and even morepreferably 4.0 to 10.0 parts by mass with respect to 100.0 parts by massof the ferromagnetic powder.

As an example of the additive which can be used in the magnetic layerincluding the abrasive, a dispersing agent disclosed in paragraphs 0012to 0022 of JP2013-131285A can be used as a dispersing agent forimproving dispersibility of the abrasive of the magnetic layer formingcomposition. It is preferable to improve dispersibility of the magneticlayer forming composition of the non-magnetic filler such as anabrasive, in order to decrease the magnetic layer surface roughness Rawhich will be described later in detail.

In addition, as the dispersing agent, a well-known dispersing agent suchas a carboxy group-containing compound or a nitrogen-containing compoundcan be used. For example, the nitrogen-containing compound may be any ofa primary amine represented by NH₂R, a secondary amine represented byNHR₂, and a tertiary amine represented by NR₃. In the above description,R represents an arbitrary structure configuring the nitrogen-containingcompound, and a plurality of Rs may be the same as each other ordifferent from each other. The nitrogen-containing compound may be acompound (polymer) having a plurality of repeating structure in amolecule. The inventors have thought that a nitrogen-containing part ofthe nitrogen-containing compound which functions as an adsorption partto the surface of the particle of the ferromagnetic hexagonal ferritepowder is a reason why the nitrogen-containing compound can function asthe dispersing agent. As the carboxy group-containing compound, fattyacid such as oleic acid can be used, for example. The inventors havethought that a carboxy group which functions as an adsorption part tothe surface of the particle of the ferromagnetic powder is a reason whythe carboxy group-containing compound can function as the dispersingagent. It is also preferable to use the carboxy group-containingcompound and the nitrogen-containing compound in combination.

Magnetic Layer Surface Roughness Ra

In the magnetic tape, in one preferred aspect, the center line averagesurface roughness Ra measured regarding the surface of the magneticlayer (magnetic layer surface roughness Ra) can be equal to or smallerthan 2.5 nm. From a viewpoint of increasing the SNR, the magnetic layersurface roughness Ra is preferably equal to or smaller than 2.5 nm. Froma viewpoint of further increasing the SNR, the magnetic layer surfaceroughness Ra is preferably equal to or smaller than 2.4 nm, morepreferably equal to or smaller than 2.3 nm, even more preferably equalto or smaller than 2.2 nm, still preferably equal to or smaller than 2.1nm, and still more preferably equal to or smaller than 2.0 nm. Inaddition, the magnetic layer surface roughness Ra can be, for example,equal to or greater than 1.0 nm or equal to or greater than 1.2 nm.However, from a viewpoint of increasing the SNR at the time of reading aservo pattern, a low magnetic layer surface roughness Ra is preferable,and thus, the magnetic layer surface roughness Ra may be lower than thelower limit exemplified above.

The center line average surface roughness Ra measured regarding thesurface of the magnetic layer of the magnetic tape in the invention andthe specification is a value measured with an atomic force microscope(AFM) in a region having an area of 40 μm×40 μm of the surface of themagnetic layer. As an example of the measurement conditions, thefollowing measurement conditions can be used. The magnetic layer surfaceroughness Ra shown in examples which will be described later is a valueobtained by the measurement under the following measurement conditions.

The measurement is performed regarding the region of 40 μm×40 μm of thearea of the surface of the magnetic layer of the magnetic tape with anAFM (Nanoscope 4 manufactured by Veeco Instruments, Inc.) in a tappingmode. RTESP-300 manufactured by BRUKER is used as a probe, a scan speed(probe movement speed) is set as 40 μm/sec, and a resolution is set as512 pixel×512 pixel.

The magnetic layer surface roughness Ra can be controlled by awell-known method. For example, the magnetic layer surface roughness Racan be changed in accordance with the size of various powders includedin the magnetic layer or manufacturing conditions of the magnetic tape.Thus, by adjusting one or more of these, it is possible to control themagnetic layer surface roughness Ra.

Non-Magnetic Layer

Next, the non-magnetic layer will be described. The magnetic tape mayinclude a magnetic layer directly on a non-magnetic support, or mayinclude a non-magnetic layer including non-magnetic powder and a bindingagent between the non-magnetic support and the magnetic layer. Thenon-magnetic powder used in the non-magnetic layer may be powder ofinorganic substances or powder of organic substances. In addition,carbon black and the like can be used. Examples of the inorganicsubstances include metal, metal oxide, metal carbonate, metal sulfate,metal nitride, metal carbide, and metal sulfide. These non-magneticpowder can be purchased as a commercially available product or can bemanufactured by a well-known method. For details thereof, descriptionsdisclosed in paragraphs 0146 to 0150 of JP2011-216149A can be referredto. For carbon black which can be used in the non-magnetic layer,descriptions disclosed in paragraphs 0040 and 0041 of JP2010-24113A canbe referred to. The content (filling percentage) of the non-magneticpowder of the non-magnetic layer is preferably 50 to 90 mass % and morepreferably 60 to 90 mass %.

In regards to other details of a binding agent or additives of thenon-magnetic layer, the well-known technology regarding the non-magneticlayer can be applied. In addition, in regards to the type and thecontent of the binding agent, and the type and the content of theadditive, for example, the well-known technology regarding the magneticlayer can be applied.

The non-magnetic layer of the magnetic tape also includes asubstantially non-magnetic layer including a small amount offerromagnetic powder as impurities or intentionally, together with thenon-magnetic powder. Here, the substantially non-magnetic layer is alayer having a residual magnetic flux density equal to or smaller than10 mT, a layer having coercivity equal to or smaller than 7.96 kA/m (100Oe), or a layer having a residual magnetic flux density equal to orsmaller than 10 mT and coercivity equal to or smaller than 7.96 kA/m(100 Oe). It is preferable that the non-magnetic layer does not have aresidual magnetic flux density and coercivity.

Non-Magnetic Support

Next, the non-magnetic support will be described. As the non-magneticsupport (hereinafter, also simply referred to as a “support”),well-known components such as polyethylene terephthalate, polyethylenenaphthalate, polyamide, polyamide imide, aromatic polyamide subjected tobiaxial stretching are used. Among these, polyethylene terephthalate,polyethylene naphthalate, and polyamide are preferable. Coronadischarge, plasma treatment, easy-bonding treatment, or heatingtreatment may be performed with respect to these supports in advance.

Back Coating Layer

The magnetic tape can also include a back coating layer includingnon-magnetic powder and a binding agent on a surface side of thenon-magnetic support opposite to the surface provided with the magneticlayer. The back coating layer preferably includes any one or both ofcarbon black and inorganic powder. In regards to the binding agentincluded in the back coating layer and various additives which can bearbitrarily included in the back coating layer, a well-known technologyregarding the treatment of the magnetic layer and/or the non-magneticlayer can be applied.

Various Thickness

A thickness of the non-magnetic support is preferably 3.00 to 6.00 μm.

A thickness of the magnetic layer is preferably equal to or smaller than0.15 μm and more preferably equal to or smaller than 0.10 μm, from aviewpoint of realization of high-density recording required in recentyears. The thickness of the magnetic layer is even more preferably 0.01to 0.10 μm. The magnetic layer may be at least single layer, themagnetic layer may be separated into two or more layers having differentmagnetic properties, and a configuration of a well-known multilayeredmagnetic layer can be applied. A thickness of the magnetic layer in acase where the magnetic layer is separated into two or more layers is atotal thickness of the layers.

A thickness of the non-magnetic layer is, for example, 0.10 to 1.50 μmand is preferably 0.10 to 1.00 μm.

Meanwhile, the magnetic tape is normally used to be accommodated andcirculated in a magnetic tape cartridge. In order to increase recordingcapacity for 1 reel of the magnetic tape cartridge, it is desired toincrease a total length of the magnetic tape accommodated in 1 reel ofthe magnetic tape cartridge. In order to increase the recordingcapacity, it is necessary that the magnetic tape is thinned(hereinafter, referred to as “thinning”). As one method of thinning themagnetic tape, a method of decreasing a total thickness of a magneticlayer and a non-magnetic layer of a magnetic tape including thenon-magnetic layer and the magnetic layer on a non-magnetic support inthis order is used. In a case where the magnetic tape includes anon-magnetic layer, the total thickness of the magnetic layer and thenon-magnetic layer is preferably equal to or smaller than 1.80 μm, morepreferably equal to or smaller than 1.50 μm, and even more preferablyequal to or smaller than 1.10 μm, from a viewpoint of thinning themagnetic tape. In addition, the total thickness of the magnetic layerand the non-magnetic layer can be, for example, equal to or greater than0.10 μm.

A thickness of the back coating layer is preferably equal to or smallerthan 0.90 μm and even more preferably 0.10 to 0.70 μm.

The thicknesses of various layers of the magnetic tape and thenon-magnetic support can be acquired by a well-known film thicknessmeasurement method. As an example, a cross section of the magnetic tapein a thickness direction is, for example, exposed by a well-known methodof ion beams or microtome, and the exposed cross section is observedwith a scanning electron microscope. In the cross section observation,various thicknesses can be acquired as a thickness acquired at oneposition of the cross section in the thickness direction, or anarithmetical mean of thicknesses acquired at a plurality of positions oftwo or more positions, for example, two positions which are arbitrarilyextracted. In addition, the thickness of each layer may be acquired as adesigned thickness calculated according to the manufacturing conditions.

Manufacturing Method

Preparation of Each Layer Forming Composition

Each composition for forming the magnetic layer, the non-magnetic layer,or the back coating layer normally includes a solvent, together withvarious components described above. As the solvent, various organicsolvents generally used for manufacturing a coating type magneticrecording medium can be used. Among those, from a viewpoint ofsolubility of the binding agent normally used in the coating typemagnetic recording medium, each layer forming composition preferablyincludes one or more ketone solvents such as acetone, methyl ethylketone, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone,isophorone, and tetrahydrofuran. The amount of the solvent of each layerforming composition is not particularly limited, and can be set to bethe same as that of each layer forming composition of a typical coatingtype magnetic recording medium. In addition, steps of preparing eachlayer forming composition generally include at least a kneading step, adispersing step, and a mixing step provided before and after thesesteps, if necessary. Each step may be divided into two or more stages.All of raw materials used in the invention may be added at an initialstage or in a middle stage of each step. In addition, each raw materialmay be separately added in two or more steps. For example, a bindingagent may be separately added in a kneading step, a dispersing step, anda mixing step for adjusting viscosity after the dispersion. In amanufacturing step of the magnetic tape, a well-known manufacturingtechnology of the related art can be used in a part of the step or inthe entire step. In the kneading step, an open kneader, a continuouskneader, a pressure kneader, or a kneader having a strong kneading forcesuch as an extruder is preferably used. The details of the kneadingprocesses of these kneaders are disclosed in JP1989-106338A(JP-H01-106338A) and JP1989-79274A (JP-H01-79274A). In addition, inorder to disperse each layer forming composition, glass beads and/orother beads can be used. As such dispersion beads, zirconia beads,titania beads, and steel beads which are dispersion beads having highspecific gravity are preferable. These dispersion beads are preferablyused by optimizing a bead diameter and a filling percentage. As adispersing machine, a well-known dispersing machine can be used. Eachlayer forming composition may be filtered by a well-known method beforeperforming the coating step. The filtering can be performed by using afilter, for example. As the filter used in the filtering, a filterhaving a hole diameter of 0.01 to 3 μm can be used, for example.

Regarding the dispersion process of the magnetic layer formingcomposition, it is preferable to prevent the occurrence of chipping asdescribed above. In order to realize the prevention, it is preferable toperform the dispersion process of the ferromagnetic hexagonal ferritepowder by a dispersion process having two stages, in which a coarseaggregate of the ferromagnetic hexagonal ferrite powder is crushed bythe dispersion process in a first stage, and the dispersion process in asecond stage, in which a collision energy applied to particles of theferromagnetic hexagonal ferrite powder due to collision with thedispersion beads is smaller than that in the first dispersion process,is performed, in the step of preparing the magnetic layer formingcomposition. According to such a dispersion process, it is possible toimprove dispersibility of the ferromagnetic hexagonal ferrite powder andprevent the occurrence of chipping.

As a preferred aspect of the dispersion process having two stages, adispersion process including a first stage of obtaining a dispersionliquid by performing the dispersion process of the ferromagnetichexagonal ferrite powder, the binding agent, and the solvent under thepresence of first dispersion beads, and a second stage of performing thedispersion process of the dispersion liquid obtained in the first stageunder the presence of second dispersion beads having smaller beaddiameter and density than those of the first dispersion beads can beused. Hereinafter, the dispersion process of the preferred aspectdescribed above will be further described.

In order to increase the dispersibility of the ferromagnetic hexagonalferrite powder, the first stage and the second stage are preferablyperformed as the dispersion process before mixing the ferromagnetichexagonal ferrite powder and other powder components. For example, in acase of forming the magnetic layer including the non-magnetic filler,the first stage and the second stage are preferably performed as adispersion process of a solution (magnetic solution) includingferromagnetic hexagonal ferrite powder, a binding agent, a solvent, andarbitrarily added additives, before mixing the non-magnetic filler.

A bead diameter of the second dispersion bead is preferably equal to orsmaller than 1/100 and more preferably equal to or smaller than 1/500 ofa bead diameter of the first dispersion bead. The bead diameter of thesecond dispersion bead can be, for example, equal to or greater than1/10,000 of the bead diameter of the first dispersion bead. However,there is no limitation to this range. The bead diameter of the seconddispersion bead is, for example, preferably 80 to 1,000 nm. Meanwhile,the bead diameter of the first dispersion bead can be, for example, 0.2to 1.0 mm.

The bead diameter of the invention and the specification is a valuemeasured by the same method as the measurement method of the averageparticle size of the powder described above.

The second stage is preferably performed under the conditions in whichthe amount of the second dispersion beads is equal to or greater than 10times of the amount of the ferromagnetic hexagonal ferrite powder, andis more preferably performed under the conditions in which the amount ofthe second dispersion beads is 10 times to 30 times of the amount of theferromagnetic hexagonal ferrite powder, based on mass.

Meanwhile, the amount of the dispersion beads in the first stage ispreferably in the range described above.

The second dispersion beads are beads having lower density than that ofthe first dispersion beads. The “density” is obtained by dividing themass (unit: g) of the dispersion beads by volume (unit: cm³). Themeasurement is performed by the Archimedes method. The density of thesecond dispersion beads is preferably equal to or lower than 3.7 g/cm³and more preferably equal to or lower than 3.5 g/cm³. The density of thesecond dispersion beads may be, for example, equal to or higher than 2.0g/cm³ or may be lower than 2.0 g/cm³. As the preferred second dispersionbeads from a viewpoint of density, diamond beads, silicon carbide beads,or silicon nitride beads can be used, and as preferred second dispersionbeads from a viewpoint of density and hardness, diamond beads can beused.

Meanwhile, as the first dispersion beads, dispersion beads havingdensity exceeding 3.7 g/cm³ are preferable, dispersion beads havingdensity equal to or higher than 3.8 g/cm³ are more preferable, anddispersion beads having density equal to or higher than 4.0 g/cm³ areeven more preferable. The density of the first dispersion beads may be,for example, equal to or smaller than 7.0 g/cm³ or may exceed 7.0 g/cm³.As the first dispersion beads, zirconia beads or alumina beads arepreferably used, and zirconia beads are more preferably used.

The dispersion time is not particularly limited and may be set inaccordance with the kind of a dispersing machine used.

Coating Step

The magnetic layer can be formed by directly applying the magnetic layerforming composition onto the surface of the non-magnetic support orperforming multilayer coating of the magnetic layer forming compositionwith the non-magnetic layer forming composition in order or at the sametime. The back coating layer can be formed by applying the back coatinglayer forming composition to the surface side of the non-magneticsupport opposite to a surface side provided with the magnetic layer (orto be provided with the magnetic layer). For details of the coating forforming each layer, a description disclosed in a paragraph 0066 ofJP2010-231843A can be referred to.

Other Steps

For details of various other steps for manufacturing the magnetic tape,descriptions disclosed in paragraphs 0067 to 0070 of JP2010-231843A canbe referred to. It is preferable that the coating layer of the magneticlayer forming composition is subjected to an orientation process, whilethe coating layer is wet (not dried). For the orientation process,various well-known technologies such as a description disclosed in aparagraph 0067 of JP2010-231843A can be used without any limitation. Asdescribed above, it is preferable to perform the homeotropic alignmentprocess as the orientation process, from a viewpoint of controlling theXRD intensity ratio. Regarding the orientation process, the abovedescription can also be referred to.

As described above, it is possible to obtain a magnetic tape included inthe magnetic tape device according to one aspect of the invention.However, the manufacturing method described above is merely an example,the XRD intensity ratio and the vertical direction squareness ratio canbe controlled to be in respective ranges described above by an arbitrarymethod capable of adjusting the XRD intensity ratio and the verticaldirection squareness ratio, and such an aspect is also included in theinvention.

Formation of Servo Pattern

A servo pattern is formed in the magnetic layer by magnetizing aspecific position of the magnetic layer with a servo pattern recordinghead (also referred to as a “servo write head”). A well-known technologyregarding a servo pattern of the magnetic layer of the magnetic tapewhich is well known can be applied for the shapes of the servo patternwith which the head tracking servo can be performed and the dispositionthereof in the magnetic layer. For example, as a head tracking servosystem, a timing-based servo system and an amplitude-based servo systemare known. The servo pattern of the magnetic layer of the magnetic tapemay be a servo pattern capable of allowing head tracking servo of anysystem. In addition, a servo pattern capable of allowing head trackingservo in the timing-based servo system and a servo pattern capable ofallowing head tracking servo in the amplitude-based servo system may beformed in the magnetic layer.

The magnetic tape described above is generally accommodated in amagnetic tape cartridge and the magnetic tape cartridge is mounted inthe magnetic tape device. In the magnetic tape cartridge, the magnetictape is generally accommodated in a cartridge main body in a state ofbeing wound around a reel. The reel is rotatably provided in thecartridge main body. As the magnetic tape cartridge, a single reel typemagnetic tape cartridge including one reel in a cartridge main body anda twin reel type magnetic tape cartridge including two reels in acartridge main body are widely used. In a case where the single reeltype magnetic tape cartridge is mounted in the magnetic tape device(drive) in order to record and/or reproduce information (magneticsignals) to the magnetic tape, the magnetic tape is drawn from themagnetic tape cartridge and wound around the reel on the drive side. Aservo head is disposed on a magnetic tape transportation path from themagnetic tape cartridge to a winding reel. Sending and winding of themagnetic tape are performed between a reel (supply reel) on the magnetictape cartridge side and a reel (winding reel) on the drive side. In themeantime, the servo head comes into contact with and slides on thesurface of the magnetic layer of the magnetic tape, and accordingly, thereading of the servo pattern is performed by the servo head. Withrespect to this, in the twin reel type magnetic tape cartridge, bothreels of the supply reel and the winding reel are provided in themagnetic tape cartridge. The magnetic tape according to one aspect ofthe invention may be accommodated in any of single reel type magnetictape cartridge and twin reel type magnetic tape cartridge. Theconfiguration of the magnetic tape cartridge is well known.

Servo Head

The magnetic tape device includes the TMR head as the servo head. Amagnetoresistance effect which is an operating principle of the MR headsuch as the TMR head is a phenomenon in which electric resistancechanges depending on a change in magnetic field. The MR head detects achange in leakage magnetic field generated from a magnetic recordingmedium such as a magnetic tape as a change in resistance value (electricresistance) and reads a servo pattern by converting the change inresistance value into a change in voltage. The tunnel magnetoresistanceeffect type element (TMR element) included in the TMR head can play arole of detecting a change in leakage magnetic field from the magnetictape as a change in resistance value (electric resistance) by using atunnel magnetoresistance effect, as a servo pattern reading element forreading a servo pattern formed in the magnetic layer of the magnetictape. By converting the detected change in resistance value into achange in voltage, the servo pattern can be read (servo signal can bereproduced).

As the TMR head included in the magnetic tape device, a TMR head havinga well-known configuration including a tunnel magnetoresistance effecttype element (TMR element) can be used. For example, for details of thestructure of the TMR head, materials of each unit configuring the TMRhead, and the like, well-known technologies regarding the TMR head canbe used.

The TMR head is a so-called thin film head. The TMR element included inthe TMR head at least includes two electrode layers, a tunnel barrierlayer, a free layer, and a fixed layer. The TMR head includes a TMRelement in a state where cross sections of these layers face a side of asurface sliding on the magnetic tape. The tunnel barrier layer ispositioned between the two electrode layers and the tunnel barrier layeris an insulating layer. Meanwhile, the free layer and the fixed layerare magnetic layers. The free layer is also referred to as amagnetization free layer and is a layer in which a magnetizationdirection changes depending on the external magnetic field. On the otherhand, the fixed layer is a layer in which a magnetization direction doesnot change depending on the external magnetic field. The tunnel barrierlayer (insulating layer) is positioned between the two electrodes,normally, and thus, even in a case where a voltage is applied, ingeneral, a current does not flow or does not substantially flow.However, a current (tunnel current) flows by the tunnel effect dependingon a magnetization direction of the free layer affected by a leakagemagnetic field from the magnetic tape. The amount of a tunnel currentflow changes depending on a relative angle of a magnetization directionof the fixed layer and a magnetization direction of the free layer, andas the relative angle decreases, the amount of the tunnel current flowincreases. A change in amount of the tunnel current flow is detected asa change in resistance value by the tunnel magnetoresistance effect. Byconverting the change in resistance value into a change in voltage, theservo pattern can be read. For an example of the configuration of theTMR head, a description disclosed in FIG. 1 of JP2004-185676A can bereferred to, for example. However, there is no limitation to the aspectshown in the drawing. FIG. 1 of JP2004-185676A shows two electrodelayers and two shield layers. Here, a TMR head having a configuration inwhich the shield layer serves as an electrode layer is also well knownand the TMR head having such a configuration can also be used. In theTMR head, a current (tunnel current) flows between the two electrodesand thereby changing electric resistance, by the tunnelmagnetoresistance effect.

Examples of a structure of the MR head include a current-in-plane (CIP)structure and a current-perpendicular-to-plane (CPP) structure. Forexample, a spin valve type GMR head which is widely used in recent yearsamong the GMR heads has a CIP structure. In the MR head having a CIPstructure, a current flows in a direction in a film plane of an MRelement, that is, a direction perpendicular to a direction in which themagnetic tape is transported, in a case of reproducing informationrecorded on the magnetic tape. With respect to this, in the MR headhaving a CPP structure, a current flows in a direction perpendicular toa film surface of an MR element, that is, a direction in which themagnetic tape is transported, in a case of reproducing informationrecorded on the magnetic tape. The TMR head is the MR head having a CPPstructure.

In one preferred aspect of the magnetic tape device including the TMRhead and the magnetic tape described above, it is possible to performthe head tracking servo by using the TMR head as the servo head in acase of recording information on the magnetic layer having a servopattern at linear recording density equal to or greater than 250 kfciand/or reproducing information recorded. The unit, kfci, is a unit oflinear recording density (not able to convert to the SI unit system).The linear recording density can be, for example, equal to or greaterthan 250 kfci and can also be equal to or greater than 300 kfci. Thelinear recording density can be, for example, equal to or smaller than800 kfci and can also exceed 800 kfci. In the magnetic tape forhigh-density recording, a width of the servo band tends to decrease, inorder to provide a large amount of data bands in the magnetic layer, andthus, the SNR at the time of reading a servo pattern easily decrease.However, a decrease in SNR can be prevented by setting the XRD intensityratio and the vertical direction squareness ratio of the magnetic tapein the magnetic tape device to be in the ranges described above.

The servo head is a magnetic head including at least the TMR element asa servo pattern reading element. The servo head may include or may notinclude a reproducing element for reproducing information recorded onthe magnetic tape. That is, the servo head and the reproducing head maybe one magnetic head or separated magnetic heads. The same applies to arecording element for performing the recording of information in themagnetic tape.

Head Tracking Servo Method

One aspect of the invention relates to a head tracking servo methodincluding: reading a servo pattern of a magnetic layer of a magnetictape by a servo head in a magnetic tape device, in which the servo headis a magnetic head including a tunnel magnetoresistance effect typeelement as a servo pattern reading element, the magnetic tape includes anon-magnetic support, and a magnetic layer including ferromagneticpowder and a binding agent on the non-magnetic support, the magneticlayer includes the servo pattern, the ferromagnetic powder isferromagnetic hexagonal ferrite powder, an intensity ratio(Int(110)/Int(114)) of a peak intensity Int(110) of a diffraction peakof a (110) plane with respect to a peak intensity Int(114) of adiffraction peak of a (114) plane of a hexagonal ferrite crystalstructure obtained by an X-ray diffraction analysis of the magneticlayer by using an In-Plane method, that is, an XRD intensity ratio is0.5 to 4.0, and a vertical direction squareness ratio of the magnetictape is 0.65 to 1.00. The reading of the servo pattern is performed bybringing the magnetic tape into contact with the servo head allowingsliding while transporting (causing running of) the magnetic tape. Thedetails of the magnetic tape and the servo head used in the headtracking servo method are as the descriptions regarding the magnetictape device according to one aspect of the invention.

Hereinafter, as one specific aspect of the head tracking servo, headtracking servo in the timing-based servo system will be described.However, the head tracking servo of the invention is not limited to thefollowing specific aspect.

In the head tracking servo in the timing-based servo system(hereinafter, referred to as a “timing-based servo”), a plurality ofservo patterns having two or more different shapes are formed in amagnetic layer, and a position of a servo head is recognized by aninterval of time in a case where the servo head has read the two servopatterns having different shapes and an interval of time in a case wherethe servo head has read two servo patterns having the same shapes. Theposition of the magnetic head of the magnetic tape in the widthdirection is controlled based on the position of the servo headrecognized as described above. In one aspect, the magnetic head, theposition of which is controlled here, is a magnetic head (reproducinghead) which reproduces information recorded on the magnetic tape, and inanother aspect, the magnetic head is a magnetic head (recording head)which records information in the magnetic tape.

FIG. 1 shows an example of disposition of data bands and servo bands. InFIG. 1, a plurality of servo bands 10 are disposed to be interposedbetween guide bands 12 in a magnetic layer of a magnetic tape 1. Aplurality of regions 11 each of which is interposed between two servobands are data bands. The servo pattern is a magnetized region and isformed by magnetizing a specific region of the magnetic layer by a servowrite head. The region magnetized by the servo write head (positionwhere a servo pattern is formed) is determined by standards. Forexample, in an LTO Ultrium format tape which is based on a localstandard, a plurality of servo patterns tilted in a tape width directionas shown in FIG. 2 are formed on a servo band in a case of manufacturinga magnetic tape. Specifically, in FIG. 2, a servo frame SF on the servoband 10 is configured with a servo sub-frame 1 (SSF1) and a servosub-frame 2 (SSF2). The servo sub-frame 1 is configured with an A burst(in FIG. 2, reference numeral A) and a B burst (in FIG. 2, referencenumeral B). The A burst is configured with servo patterns A1 to A5 andthe B burst is configured with servo patterns B1 to B5. Meanwhile, theservo sub-frame 2 is configured with a C burst (in FIG. 2, referencenumeral C) and a D burst (in FIG. 2, reference numeral D). The C burstis configured with servo patterns C1 to C4 and the D burst is configuredwith servo patterns D1 to D4. Such 18 servo patterns are disposed in thesub-frames in the arrangement of 5, 5, 4, 4, as the sets of 5 servopatterns and 4 servo patterns, and are used for recognizing the servoframes. FIG. 2 shows one servo frame for explaining. However, inpractice, in the magnetic layer of the magnetic tape in which the headtracking servo in the timing-based servo system is performed, aplurality of servo frames are disposed in each servo band in a runningdirection. In FIG. 2, an arrow shows the running direction. For example,an LTO Ultrium format tape generally includes 5,000 or more servo framesper a tape length of 1 m, in each servo band of the magnetic layer. Theservo head sequentially reads the servo patterns in the plurality ofservo frames, while coming into contact with and sliding on the surfaceof the magnetic layer of the magnetic tape transported in the magnetictape device.

In the head tracking servo in the timing-based servo system, a positionof a servo head is recognized based on an interval of time in a casewhere the servo head has read the two servo patterns (reproduced servosignals) having different shapes and an interval of time in a case wherethe servo head has read two servo patterns having the same shapes. Thetime interval is normally obtained as a time interval of a peak of areproduced waveform of a servo signal. For example, in the aspect shownin FIG. 2, the servo pattern of the A burst and the servo pattern of theC burst are servo patterns having the same shapes, and the servo patternof the B burst and the servo pattern of the D burst are servo patternshaving the same shapes. The servo pattern of the A burst and the servopattern of the C burst are servo patterns having the shapes differentfrom the shapes of the servo pattern of the B burst and the servopattern of the D burst. An interval of the time in a case where the twoservo patterns having different shapes are read by the servo head is,for example, an interval between the time in a case where any servopattern of the A burst is read and the time in a case where any servopattern of the B burst is read. An interval of the time in a case wherethe two servo patterns having the same shapes are read by the servo headis, for example, an interval between the time in a case where any servopattern of the A burst is read and the time in a case where any servopattern of the C burst is read. The head tracking servo in thetiming-based servo system is a system supposing that occurrence of adeviation of the time interval is due to a position change of themagnetic tape in the width direction, in a case where the time intervalis deviated from the set value. The set value is a time interval in acase where the magnetic tape runs without occurring the position changein the width direction. In the timing-based servo system, the magnetichead is moved in the width direction in accordance with a degree of thedeviation of the obtained time interval from the set value.Specifically, as the time interval is greatly deviated from the setvalue, the magnetic head is greatly moved in the width direction. Thispoint is applied to not only the aspect shown in FIGS. 1 and 2, but alsoto entire timing-based servo systems.

For the details of the head tracking servo in the timing-based servosystem, well-known technologies such as technologies disclosed in U.S.Pat. No. 5,689,384A, U.S. Pat. No. 6,542,325B, and U.S. Pat. No.7,876,521B can be referred to, for example. In addition, for the detailsof the head tracking servo in the amplitude-based servo system,well-known technologies disclosed in U.S. Pat. No. 5,426,543A and U.S.Pat. No. 5,898,533A can be referred to, for example.

According to one aspect of the invention, a magnetic tape used in amagnetic tape device in which a TMR head is used as a servo head, themagnetic tape including: a magnetic layer including ferromagnetic powderand a binding agent on a non-magnetic support, in which the magneticlayer includes a servo pattern, the ferromagnetic powder isferromagnetic hexagonal ferrite powder, an XRD intensity ratio is 0.5 to4.0, and a vertical direction squareness ratio is 0.65 to 1.00, is alsoprovided. The details of the magnetic tape are also as the descriptionsregarding the magnetic tape device according to one aspect of theinvention.

EXAMPLES

Hereinafter, the invention will be described with reference to examples.However, the invention is not limited to aspects shown in the examples.“Parts” and “%” in the following description mean “parts by mass” and“mass %”, unless otherwise noted. In addition, steps and evaluationsdescribed below are performed in an environment of an atmospheretemperature of 23° C.±1° C., unless otherwise noted.

Example 1

1. Manufacturing of Magnetic Tape

A list of components of each layer forming composition is shown below.

List of Components of Magnetic Layer Forming Composition

Magnetic Solution

Plate-shaped ferromagnetic hexagonal ferrite powder (M-type bariumferrite): 100.0 parts

-   -   (Activation volume: 1,500 nm³)

Oleic acid: 2.0 parts

A vinyl chloride copolymer (MR-104 manufactured by Zeon Corporation):10.0 parts

SO₃Na group-containing polyurethane resin: 4.0 parts

-   -   (Weight-average molecular weight: 70,000, SO₃Na group: 0.07        meq/g)

An amine-based polymer (DISPERBYK-102 manufactured by BYK Additives &Instruments): 6.0 parts

Methyl ethyl ketone: 150.0 parts

Cyclohexanone: 150.0 parts

Abrasive Liquid

α-alumina: 6.0 parts

1 (BET specific surface area: 19 m²/g, Mohs hardness: 9)

SO₃Na group-containing polyurethane resin: 0.6 parts

-   -   (Weight-average molecular weight: 70,000, SO₃Na group: 0.1        meq/g)

2,3-Dihydroxynaphthalene: 0.6 parts

Cyclohexanone: 23.0 parts

Projection Forming Agent Liquid

Colloidal silica: 2.0 parts

-   -   (Average particle size: 80 nm)

Methyl ethyl ketone: 8.0 parts

Lubricant and Curing Agent Liquid

Stearic acid: 3.0 parts

Stearic acid amide: 0.3 parts

Butyl stearate: 6.0 parts

Methyl ethyl ketone: 110.0 parts

Cyclohexanone: 110.0 parts

Polyisocyanate (CORONATE (registered trademark) L manufactured by NipponPolyurethane Industry Co., Ltd.): 3.0 parts

List of Components of Non-Magnetic Layer Forming Composition

Non-magnetic inorganic powder: α-iron oxide: 100.0 parts

-   -   (Average particle size: 10 nm, BET specific surface area: 75        m²/g)

Carbon black: 25.0 parts

-   -   (Average particle size: 20 nm)

A SO₃Na group-containing polyurethane resin: 18.0 parts

-   -   (Weight-average molecular weight: 70,000, content of SO₃Na        group: 0.2 meq/g)

Stearic acid: 1.0 part

Cyclohexanone: 300.0 parts

Methyl ethyl ketone: 300.0 parts

List of Components of Back Coating Layer Forming Composition

Non-magnetic inorganic powder: α-iron oxide: 80.0 parts

-   -   (Average particle size: 0.15 μm, BET specific surface area: 52        m²/g)

Carbon black: 20.0 parts

-   -   (Average particle size: 20 nm)

A vinyl chloride copolymer: 13.0 parts

A sulfonic acid group-containing polyurethane resin: 6.0 parts

Phenylphosphonic acid: 3.0 parts

Cyclohexanone: 155.0 parts

Methyl ethyl ketone: 155.0 parts

Stearic acid: 3.0 parts

Butyl stearate: 3.0 parts

Polyisocyanate: 5.0 parts

Cyclohexanone: 200.0 parts

Preparation of Magnetic Layer Forming Composition

The magnetic layer forming composition was prepared by the followingmethod.

A dispersion liquid A was prepared by dispersing (first stage) variouscomponents of the magnetic solution with a batch type vertical sand millby using zirconia beads having a bead diameter of 0.5 mm (firstdispersion beads, density of 6.0 g/cm³) for 24 hours, and thenperforming filtering with a filter having a hole diameter of 0.5 μm. Theused amount of zirconia beads was 10 times of the amount of theferromagnetic hexagonal barium ferrite powder based on mass.

After that, a dispersion liquid (dispersion liquid B) was prepared bydispersing (second stage) dispersion liquid A with a batch type verticalsand mill by using diamond beads having a bead diameter shown in Table 1(second dispersion beads, density of 3.5 g/cm³) for 1 hour, and thenseparating diamond beads by using a centrifugal separator. The magneticsolution is the dispersion liquid B obtained as described above. Theused amount of diamond beads was 10 times of the amount of theferromagnetic hexagonal barium ferrite powder based on mass.

Regarding the abrasive liquid, various components of the abrasive liquidwere mixed with each other and put in a transverse bead mill dispersingdevice together with zirconia beads having a bead diameter of 0.3 mm, soas to perform the adjustment so that a value of bead volume/(abrasiveliquid volume+bead volume) was 80%, the bead mill dispersion process wasperformed for 120 minutes, the liquid after the process was extracted,and an ultrasonic dispersion filtering process was performed by using aflow type ultrasonic dispersion filtering device. By doing so, theabrasive liquid was prepared.

The magnetic layer forming composition was prepared by introducing theprepared magnetic solution, the abrasive liquid, the projection formingagent liquid, and the lubricant, and the curing agent liquid in adissolver stirrer, stirring the mixture at a circumferential speed of 10m/sec for 30 minutes, and performing a process of 3 passes at a flowrate of 7.5 kg/min with a flow type ultrasonic dispersing device, andfiltering the mixture with a filter having a hole diameter of 1 μm.

Preparation of Non-Magnetic Layer Forming Composition

A non-magnetic layer forming composition was prepared by dispersingvarious components of the non-magnetic layer forming composition with abatch type vertical sand mill by using zirconia beads having a beaddiameter of 0.1 mm for 24 hours, and then performing filtering with afilter having a hole diameter of 0.5 μm.

Preparation of Back Coating Layer Forming Composition

Components among various components of the back coating layer formingcomposition except a lubricant (stearic acid and butyl stearate),polyisocyanate, and 200.0 parts of cyclohexanone were kneaded anddiluted by an open kneader, and subjected to a dispersion process of 12passes, with a transverse beads mill dispersing device and zirconiabeads having a bead diameter of 1 mm, by setting a bead fillingpercentage as 80 volume %, a circumferential speed of rotor distal endas 10 m/sec, and a retention time for 1 pass as 2 minutes. After that,the remaining components were added and stirred with a dissolver, theobtained dispersion liquid was filtered with a filter having a holediameter of 1 μm and a back coating layer forming composition wasprepared.

Manufacturing Method of Magnetic Tape

The non-magnetic layer forming composition prepared as described abovewas applied to a surface of a support made of polyethylene naphthalatehaving a thickness of 5.00 μm so that the thickness after the dryingbecomes 1.00 μm and was dried to form a non-magnetic layer. The magneticlayer forming composition prepared as described above was applied ontothe surface of the formed non-magnetic layer so that the thickness afterthe drying becomes 70 nm (0.07 μm) and a coating layer was formed. Ahomeotropic alignment process was performed by applying a magnetic fieldhaving a strength shown in Table 1 in a vertical direction with respectto the surface of the coating layer, while the coating layer of themagnetic layer forming composition is wet (not dried). After that, thecoating layer was dried to form a magnetic layer.

After that, the back coating layer forming composition prepared asdescribed above was applied to the surface of the support on a sideopposite to the surface where the non-magnetic layer and the magneticlayer are formed, so that the thickness after the drying becomes 0.40μm, and was dried.

A calender process (surface smoothing treatment) was performed withrespect to the magnetic tape obtained as described above by a calenderconfigured of only a metal roll, at a speed of 100 m/min, linearpressure of 300 kg/cm (294 kN/m), and a surface temperature of acalender roll of 90° C., and then, a thermal treatment was performed inthe environment of the atmosphere temperature of 70° C. for 36 hours.After the thermal treatment, the slitting was performed to have a widthof ½ inches (0.0127 meters), and a magnetic tape is obtained.

By doing so, a magnetic tape for forming a servo pattern in the magneticlayer was manufactured.

In a state where the magnetic layer of the manufactured magnetic tapewas demagnetized, servo patterns having disposition and shapes accordingto the LTO Ultrium format were formed on the magnetic layer by using aservo write head mounted on a servo tester. Accordingly, a magnetic tapeincluding data bands, servo bands, and guide bands in the dispositionaccording to the LTO Ultrium format in the magnetic layer, and includingservo patterns having the disposition and the shape according to the LTOUltrium format on the servo band is manufactured. The servo testerincludes a servo write head and a servo head. This servo tester was alsoused in evaluations which will be described later.

The thickness of each layer and the thickness of the non-magneticsupport of the manufactured magnetic tape were acquired by the followingmethod, and it was confirmed that the thicknesses obtained are thethicknesses described above.

A cross section of the magnetic tape in a thickness direction wasexposed to ion beams and the exposed cross section was observed with ascanning electron microscope. Various thicknesses were obtained as anarithmetical mean of thicknesses obtained at two portions in thethickness direction in the cross section observation.

A part of the magnetic tape manufactured by the method described abovewas used in the evaluation of physical properties described below, andthe other part was used in order to measure an SNR which will bedescribed later.

The activation volume of the ferromagnetic hexagonal ferrite powderdescribed above is a value calculated by performing measurement by usinga powder lot which is the same as that of ferromagnetic hexagonalferrite powder used in the magnetic layer forming composition. Themagnetic field sweep rates in the coercivity Hc measurement part attiming points of 3 minutes and 30 minutes were measured by using anoscillation sample type magnetic-flux meter (manufactured by ToeiIndustry Co., Ltd.), and the activation volume was calculated from therelational expression described above. The measurement was performed inthe environment of 23° C.±1° C.

2. Evaluation of Physical Properties of Magnetic Tape

(1) XRD Intensity Ratio

A tape sample was cut out from the manufactured magnetic tape.

Regarding the cut-out tape sample, the surface of the magnetic layer wasirradiated with X-ray by using a thin film X-ray diffraction device(Smart Lab manufactured by Rigaku Corporation), and the In-Plane XRD wasperformed by the method described above.

The peak intensity Int(114) of the diffraction peak of the (114) planeand the peak intensity Int(110) of the diffraction peak of a (110) planeof a hexagonal ferrite crystal structure were obtained from the X-raydiffraction spectra obtained by the In-Plane XRD, and the XRD intensityratio (Int(110)/Int(114)) was calculated.

(2) Vertical Direction Squareness Ratio

A vertical direction squareness ratio of the manufactured magnetic tapewas obtained by the method described above using an oscillation sampletype magnetic-flux meter (manufactured by Toei Industry Co., Ltd.).

(3) Center Line Average Surface Roughness Ra Measured Regarding Surfaceof Magnetic Layer

The measurement regarding a measurement area of 40 μm×40 μm in thesurface of the magnetic layer of the magnetic tape was performed with anatomic force microscope (AFM, Nanoscope 4 manufactured by VeecoInstruments, Inc.) in a tapping mode, and a center line average surfaceroughness Ra was acquired. RTESP-300 manufactured by BRUKER is used as aprobe, a scan speed (probe movement speed) was set as 40 μm/sec, and aresolution was set as 512 pixel×512 pixel.

3. Measurement of SNR

In an environment of an atmosphere temperature of 23° C.±1° C. andrelative humidity of 50%, the servo head of the servo tester wasreplaced with a commercially available TMR head (element width of 70 nm)as a reproducing head for HDD. The reading of a servo pattern wasperformed by attaching the magnetic tape manufactured in the section 1.to the servo tester, and the SNR was obtained as a ratio of the outputand noise. The SNR was calculated as a relative value by setting the SNRmeasured as 0 dB in Comparative Example 1 which will be described later.In a case where the SNR calculated as described above is equal to orgreater than 2.0 dB, it is possible to evaluate that performance ofdealing with future needs accompanied with high-density recording isobtained.

Examples 2 to 5 and Comparative Examples 1 to 11

1. Manufacturing of Magnetic Tape

A magnetic tape was manufactured in the same manner as in Example 1,except that various conditions shown in Table 1 were changed as shown inTable 1.

In Table 1, in the comparative examples in which “none” is shown in acolumn of the dispersion beads and a column of the time, the magneticlayer forming composition was prepared without performing the secondstage in the magnetic solution dispersion process.

In Table 1, in the comparative examples in which “none” is shown in acolumn of the homeotropic alignment process magnetic field intensity,the magnetic layer was formed without performing the orientationprocess.

2. Evaluation of Physical Properties of Magnetic Tape

Various physical properties of the manufactured magnetic tape wereevaluated in the same manner as in Example 1.

3. Measurement of SNR

The SNR was measured by the same method as that in Example 1, by usingthe manufactured magnetic tape. In Examples 2 to 5 and ComparativeExamples 2 to 6, the TMR head which was the same as that in Example 1was used as a servo head. In Comparative Examples 1 and 7 to 11, acommercially available spin valve type GMR head (element width of 70 nm)was used as a servo head.

The results of the evaluations described above are shown in Table 1.

TABLE 1 Magnetic solution dispersion process second stage Dispersionbeads Used amount (mass of beads with respect to mass of HomeotropicMagnetic layer ferromagnetic alignment process center line average Beadhexagonal ferrite magnetic field surface roughness Kind diameter powder)Time intensity Ra Comparative Example 1 None None None None None 2.0 nmComparative Example 2 None None None None None 2.0 nm ComparativeExample 3 None None None None 0.15 T 2.0 nm Comparative Example 4 NoneNone None None 0.30 T 2.0 nm Comparative Example 5 Diamond 500 nm 10times 1 h 1.00 T 2.0 nm Comparative Example 6 Diamond 500 nm 10 times 1h None 2.0 nm Comparative Example 7 Diamond 500 nm 10 times 1 h 0.15 T2.0 nm Comparative Example 8 Diamond 500 nm 10 times 1 h 0.20 T 2.0 nmComparative Example 9 Diamond 500 nm 10 times 1 h 0.30 T 2.0 nmComparative Example 10 Diamond 500 nm 10 times 1 h 0.50 T 2.0 nmComparative Example 11 Diamond 500 nm 20 times 1 h 0.15 T 2.0 nm Example1 Diamond 500 nm 10 times 1 h 0.15 T 2.0 nm Example 2 Diamond 500 nm 10times 1 h 0.20 T 2.0 nm Example 3 Diamond 500 nm 10 times 1 h 0.30 T 2.0nm Example 4 Diamond 500 nm 10 times 1 h 0.50 T 2.0 nm Example 5 Diamond500 nm 20 times 1 h 0.15 T 2.0 nm Vertical XRD intensity ratio directionInt(110)/Int(114) squareness ratio Servo head SNR (dB) ComparativeExample 1 0.2 0.55 GMR 0 Comparative Example 2 0.2 0.55 TMR 1.0Comparative Example 3 3.8 0.63 TMR 1.4 Comparative Example 4 5.0 0.75TMR 1.3 Comparative Example 5 6.1 0.90 TMR 1.3 Comparative Example 6 0.30.66 TMR 1.1 Comparative Example 7 0.5 0.70 GMR 0.5 Comparative Example8 1.5 0.75 GMR 0.6 Comparative Example 9 2.3 0.80 GMR 0.7 ComparativeExample 10 4.0 0.85 GMR 0.8 Comparative Example 11 0.7 0.83 GMR 0.7Example 1 0.5 0.70 TMR 2.5 Example 2 1.5 0.75 TMR 2.7 Example 3 2.3 0.80TMR 3.0 Example 4 4.0 0.85 TMR 2.8 Example 5 0.7 0.83 TMR 2.7

As shown in Table 1, in Examples 1 to 5, the servo pattern could be readat a high SNR by using the TMR head as the servo head, compared toComparative Examples 1 to 11.

The invention is effective for usage of magnetic recording for whichhigh-sensitivity reproducing of information recorded with high densityis desired.

What is claimed is:
 1. A magnetic tape device comprising: a magnetictape; and a servo head, wherein the servo head is a magnetic headincluding a tunnel magnetoresistance effect type element as a servopattern reading element, the magnetic tape includes a non-magneticsupport, and a magnetic layer including ferromagnetic powder and abinding agent on the non-magnetic support, the magnetic layer includes aservo pattern, the ferromagnetic powder is ferromagnetic hexagonalferrite powder, an intensity ratio Int(110)/Int(114) of a peak intensityInt(110) of a diffraction peak of a (110) plane with respect to a peakintensity Int(114) of a diffraction peak of a (114) plane of a hexagonalferrite crystal structure obtained by an X-ray diffraction analysis ofthe magnetic layer by using an In-Plane method is 0.5 to 4.0, and avertical direction squareness ratio of the magnetic tape is 0.65 to1.00.
 2. The magnetic tape device according to claim 1, wherein thevertical direction squareness ratio of the magnetic tape is 0.65 to0.90.
 3. The magnetic tape device according to claim 1, wherein a centerline average surface roughness Ra measured regarding a surface of themagnetic layer is equal to or smaller than 2.5 nm.
 4. The magnetic tapedevice according to claim 1, wherein the magnetic tape includes anon-magnetic layer including non-magnetic powder and a binding agentbetween the non-magnetic support and the magnetic layer.
 5. A headtracking servo method comprising: reading a servo pattern of a magneticlayer of a magnetic tape by a servo head in a magnetic tape device,wherein the servo head is a magnetic head including a tunnelmagnetoresistance effect type element as a servo pattern readingelement, the magnetic tape includes a non-magnetic support, and amagnetic layer including ferromagnetic powder and a binding agent on thenon-magnetic support, the magnetic layer includes the servo pattern, theferromagnetic powder is ferromagnetic hexagonal ferrite powder, anintensity ratio Int(110)/Int(114) of a peak intensity Int(110) of adiffraction peak of a (110) plane with respect to a peak intensityInt(114) of a diffraction peak of a (114) plane of a hexagonal ferritecrystal structure obtained by an X-ray diffraction analysis of themagnetic layer by using an In-Plane method is 0.5 to 4.0, and a verticaldirection squareness ratio of the magnetic tape is 0.65 to 1.00.
 6. Thehead tracking servo method according to claim 5, wherein the verticaldirection squareness ratio of the magnetic tape is 0.65 to 0.90.
 7. Thehead tracking servo method according to claim 5, wherein a center lineaverage surface roughness Ra measured regarding a surface of themagnetic layer is equal to or smaller than 2.5 nm.
 8. The head trackingservo method according to claim 5, wherein the magnetic tape includes anon-magnetic layer including non-magnetic powder and a binding agentbetween the non-magnetic support and the magnetic layer.